This invention relates to thick film conductors employing oxides of copper.
Thick film conductors are well known in the art and are acquiring increasing importance in view of trends in the electronic industry towards smaller and smaller circuits. In the past, thick film conductors have been produced wherein the circuit was of a noble metal. By noble metal is meant gold, silver, palladium, platinum mixtures thereof and alloys thereof. More recently, considerable efforts have been expended in attempting to produce thick film conductors employing base metals such as copper, nickel, and cobalt. Examples of such efforts are described, for example, in:
U.S. Pat. No. 4,070,517 to Kazmierowicz; and PA1 U.S. Pat. No. 4,070,518 to Kazmierowicz; and PA1 U.S. Pat. No. 4,072,771 to Grier; and PA1 U.S. Pat. No. 4,079,156 to Youtsey et al; and PA1 U.S. Pat. No. 4,082,898 to Miller et al; and PA1 U.S. Pat. No. 4,122,232 to Kuo; and PA1 U.S. Pat. No. 4,140,817 to Brown; and PA1 U.S. Pat. No. 4,158,716 to Miller et al; and PA1 U.S. Pat. No. 4,172,919 to Mitchell.
Unfortunately, the prior art suffers from a number of disadvantages. The use of copper is burdensome because copper powder tends to oxidize on storage. The oxidation of copper powder on storage gives the copper powder an oxide coating which means that the powder is in reality a composition of copper and copper oxide of varying proportions depending upon the degree of oxidation.
Many commercially available substrates have limited firing temperatures. For example porcelain coated steel, glass, and glass bonded mica become soft when heated to temperatures above about 675.degree. C. Many commercially available thick film conductor pastes must be fired above 675.degree. C. which means that they cannot be employed with these substrates.
Another problem in the prior art is the great expense of copper which, although less than that of the noble metals, is nevertheless greater than desired.
Another severe problem of the prior art is the necessity of employing an inert atmosphere such as that of nitrogen or a reducing atmosphere such as that of hydrogen. Nitrogen atmospheres and the special belt furnaces necessary to employ a nitrogen atmosphere are expensive. Hydrogen atmospheres, in addition to being expensive, are potentially explosive and also require special furnaces for their utilization.
It is therefore an object of the present invention to provide an improved thick film conductor paste substantially free of one or more of the disadvantages of prior pastes.
An additional object of the present invention is to provide a process and a thick film conductor paste that can be fired in air.
Yet another object of the present invention is to provide a thick film conductor paste that can be fired at temperatures below 675.degree. C.
Another object of the present invention is to provide an improved thick film conductor paste which does not employ a noble metal.
Yet another object of the present invention is to provide an improved thick film conductor paste which does not require the presence of copper metal but will tolerate the presence of copper metal.
Yet another object of the present invention is to provide a thick film conductor paste that has a long shelf life.
Still another object of the present invention is to provide an improved method for making a thick film conductor.
Still another object of the present invention is to provide an improved thick film conductor.
Still another object of the present invention is to provide an improved thick film conductor paste capable of being fired onto substrates of glass, porcelain coated steel and glass bonded mica at a temperature below the softening temperature of the substrate.